Light-sensitive compositions containing light-sensitive diazo compounds have heretofore been widely used. These light-sensitive compositions can be divided into two groups: (1) a positive-type light-sensitive composition that upon irradiation with light, exposed areas become soluble in a developer, and (2) a negative-type light-sensitive composition that upon irradiation with light, exposed areas are insolubilized. The present invention relates to improvements in the negative-type light-sensitive composition.
As a negative-type light-sensitive diazo compound, a condensate of 4-diazodiphenylamine and formaldehyde has long been known and widely used. This condensate, however, is water-soluble and, when used in production of lithographic printing plates, for example, has disadvantages in lipophilic nature, abrasion resistance, storage stability, and so forth. For this reason, various modifications have been made.
In lithographic printing, as is well known, water is first applied to the plate surface and then an oily ink is applied. Therefore, image areas to which the ink attaches are required to have sufficiently good lipophilic nature even in the presence of water. The conventional printing plates are inferior in this lipophilic nature, and the ink fails to attach to the image areas in a short time initially. Thus, prior to practical printing, ten or more sheets of paper, sometimes several tens of sheets of paper must be printed (trial printing) before the image areas become ready receive the ink in the presence of water. This leads to a loss of time and materials. In order to reduce the loss of time and materials, it has been desired in the art to increase the lipophilic nature of image areas.
In addition, in order to produce a large number of printed matters, it is necessary that the image areas are strong; therefore, a light-sensitive material having superior abrasion resistance has been desired.
In order to satisfy the above requirements, a procedure has been proposed in which water-soluble light-sensitive diazo compounds are reacted with aromatic acid compounds such as 4-toluenesulfonic acid to prepare the corresponding diazo salts, thereby making the diazo compounds soluble in organic solvents. The resulting salts are used singly or in combination with other polymeric compounds.
When, however, the salts are used singly, no satisfactory lipophilic nature and abrasion resistance can be obtained. For this reason, as in a wipe-on plate which is well known in the field of lithographic printing, after the formation of images, it is necessary for the image areas to be reinforced with a resin solution in order to increase their lipophilic nature and abrasion resistance.
The use of diazo compounds in combination with other resins is also known as described in Japanese Patent Application (OPI) No. 118802/75 and U.S. Pat. No. 4,299,905, for example (the term "OPI" as used herein means a "published unexamined Japanese patent application").
With the light-sensitive composition described in Japanese Patent Application (OPI) No. 118802/75, sufficiently satisfactory lipophilic nature of the amount required in the field of lithographic printing cannot be obtained, although compatibility with the diazo compounds and image-forming properties are good. Moreover, acrylonitrile or methacrylonitrile copolymers are used to reduce swelling at the time of development and to increase abrasion resistance, but the strength of the copolymers is not sufficiently high. Because of this poor strength, high printing resistance that is required in printing cannot be obtained.
In the composition of U.S. Pat. No. 4,299,905, epoxy resins are used in combination for the purpose of increasing abrasion resistance. As these epoxy resins, those resins which are liquid at ordinary temperature are used. Therefore the composition has disadvantages in that under operation conditions of high temperature and high humidity a light-sensitive layer made of the composition becomes sticky, is unstable in light-sensitivity, and can be developed only in several days. In order to prevent such sticking, it is necessary to add the diazo compound in large amounts. This, naturally, leads to a reduction in rate of sensitization.